Memory devices have a wide range of uses in modern electronics and electronic devices. In general, various types of electronic memory exist, including hard disc memory, floppy disc memory, magnetic tape memory, optical disk memory, and so on. One of the more innovative and diversified types of memory is semiconductor memory.
One type of semiconductor memory commonly used for modern electronics is nonvolatile Flash memory. Flash memory comprises arrays of semiconductor memory transistors that can be utilized to store, erase and re-store digital information. Compared to other types of electronic memory, Flash memory is fast both in terms of programming and erasing, as well as reading data, has good data retention characteristics, and is highly cost effective. Accordingly, Flash memory is utilized for data storage in an ever-increasing number of electronic devices and applications, including computers, cell phones, smart-phones, digital cameras and camcorders, game stations, and so forth.
Early forms of semiconductor memory required continuous access to electrical power to enable data retention. For instance, volatile semiconductor memory requires an external voltage to be applied on one region of a memory transistor to maintain a stored charge in another region of the memory transistor. If the external voltage drops below a required level, the stored charge is lost. For a volatile memory device, such as random access memory (RAM), the lost charge results in lost data. Although volatile semiconductor memory has significant advantages, including high program and read speeds, the threat of data loss has made volatile semiconductor memory suitable primarily for RAM applications, especially given non-volatile mass storage alternatives such as hard drives, disc drives, and so on.
One great advantage of Flash memory is that stored data can be retained without continuous electrical power applied to a Flash memory module. In addition, Flash memory is a solid-state technology that can be very dense—in terms of memory cells per unit volume—typically requiring no moving parts for basic operation. Accordingly, Flash memory is ideal as removable and portable data storage for consumer electronics, and is utilized with universal interface technologies for a wide array of electronic devices, such as universal serial bus (USB) technology. The non-volatile nature of Flash memory suggests employing Flash for RAM applications. However, RAM is typically faster and more compact than Flash, and consumes relatively low power. Thus, additional improvements in Flash density and speed would be required to employ Flash memory as a RAM replacement in many devices and applications.
One area where Flash has made successful inroads is in hard disc replacement. Hard discs are non-volatile and have very high storage capacity, but often have slower read and write times than Flash memory devices and have moving mechanical parts that are much less shock resistant than semiconductor-based memory. Accordingly, computer and electronic devices can achieve performance and reliability improvements when utilizing a non-volatile semiconductor hard drive, such as a Flash hard drive.
To achieve performance improvements, new designs generally aim to reduce time required to program, erase and read Flash memory cells. This equates to faster memory access times, a desired trait for digital memory. Another goal is to provide improved memory density; in effect increasing a number of storable bits per volume of semiconductor space. Yet another goal of Flash memory research is to improve data retention capability, mitigating data loss that occurs over time. And of course, a general goal is to provide a suitable aggregate of the foregoing or similar improvements (e.g., scalability, multi-layer capability, power consumption, or the like), yielding a Flash memory device that is highly preferable for various electronic device applications.
Because different Flash memory designs have different characteristics, however, utilizing one design may provide fast program and erase times, but slow read times. Another design may provide fast read times, but slow program times, or reduced data longevity, and so on. One objective of the subject disclosure is to provide a Flash memory device that provides an aggregate of advantages of conventional Flash memory. Another objective is to provide Flash memory that has fast program, erase and read times, compared with conventional Flash memory, with similar or improved memory density. Yet another objective is to provide a mechanism for fabricating improved Flash memory based on the foregoing objectives.